Plasma processing method and apparatus, and storage medium

ABSTRACT

A plasma processing method performs a plasma processing on a substrate mounted on a mounting table installed in an airtight processing chamber, the mounting table having a smaller size than the substrate. The substrate having a surface, on which a resist mark is formed, is mounted on the mounting table and then electrostatically adsorbed on the mounting table by applying a voltage to an electrostatic chuck. The surface of the substrate is etched by using a plasma of an etching gas while the substrate is cooled through a heat transfer between the substrate and the mounting table via a thermally conductive gas supplied between a top surface of the mounting table and a bottom surface of the substrate. The supply of the thermally conductive gas is stopped, and the resist mask on the substrate is ashed by using a plasma of an ashing gas containing 0 2 .

CROSS REFERENCE

This application is a divisional of and claims the benefit of priorityunder 35 U.S.C § 120 from U.S. application Ser. No. 11/235,341, filedSep. 27, 2005, which is a Non-Provisional of U.S. Application Ser. No.60/620,349, filed Oct. 21, 2004, and claims the benefit of priorityunder 35 U.S.C. § 119 of Japanese Patent Application No. 2004-279432,filed Sep. 27, 2004. The entire contents of these applications areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a plasma processing method andapparatus for performing an etching process by using a plasma of anetching gas and an ashing process by using a plasma of an ashing gas,and a storage medium.

BACKGROUND OF THE INVENTION

In a semiconductor device manufacturing process, in order to separate acapacitor or a device or to form a contact hole, a dry etching isperformed on a substrate, e.g., a semiconductor wafer (hereinafter,referred to as “wafer”), on which a resist mask is formed, and, then, anashing process is carried out to remove the resist remaining on thesurface after the etching process. As one of methods for performing suchprocesses, there has been known a plasma processing method employed in asingle sheet parallel plate type plasma processing apparatus.

Hereinafter, a schematic constitution of such plasma processingapparatus will be briefly described with reference to FIG. 6. In such aplasma processing apparatus, an upper electrode 11 serving as a gasshower head and a mounting table 12 serving as a lower electrode andalso as a cooling plate are installed at an upper and a lower portion ina processing chamber 10 having a vacuum exhaust unit 10, respectively,and a high frequency power supply 13 for forming a high frequencyelectric field between the electrodes is connected to the upperelectrode 11. Further, a wafer mounting region on an electrostatic chuck14 installed on top of the mounting table 12 is formed smaller than asize of a wafer W. A ring member 15, e.g., a quartz ring, is installedso as to surround an entire circumference of the electrostatic chuck 14.The ring member 15 is disposed to face a side peripheral surface and abottom peripheral portion of the wafer W protruded outwardly from themounting region with a gap formed therebetween. Moreover, formed on asurface of the electrostatic chuck 14 are gas supply openings (notshown) for supplying a thermally conductive He gas to be outwardlydiffused from a central portion through gaps formed by slightirregularities on surfaces of the wafer W and the electrostatic chuck14.

Mounted on the mounting table 12 is the wafer W on which an insulatingfilm made of, e.g., SiO₂ and a resist mask of a circuit pattern arelaminated. Further, a chuck voltage is applied to the electrostaticchuck 14 and an inner space of the processing chamber 1 isvacuum-exhausted by a vacuum exhaust unit 10. In such state, an etchinggas containing a compound of C and F (e.g., CxFy) is plasmarized,thereby etching the insulating film. Next, a supply of the etching gasis stopped and an ashing gas containing O₂ is then supplied into theprocessing chamber 1. The ashing gas is plasmarized by forming a highfrequency electric field, so that the resist exposed to the plasma isashed and removed. Accordingly, after having undergone such processes,the insulating film on the wafer W has therein grooves corresponding tothe circuit pattern.

However, if the etching process is performed by using a plasma of aCF-based gas, as schematically illustrated in FIG. 7, a polymer mainlycomposed of CFx, which is generated by a decomposition or a reaction ofthe etching gas, is adhered to the bottom peripheral portion and theside edge surface of the wafer W. In other words, the mounting table 12is formed in a smaller size than the wafer W to prevent damagesinflicted by the etching gas. Further, in general, the ring member 15,referred to as, e.g., a focus ring, for adjusting a plasma shape isinstalled so as to surround the wafer W. In order to prevent the gasfrom flowing toward the bottom surface of the wafer W, a stepped portion15 a is formed at an inner side of the ring member 15 such that itextends into a space under the bottom surface of the wafer W. However,it is not sufficient to prevent the plasma from flowing into the space,so that deposits of the polymer are adhered to the bottom peripheralportion of the wafer W.

In the ashing process after the etching process, the plasma of theashing gas containing O₂ flows into the aforementioned space along aslight gap between the peripheral portion of the wafer W and the ringmember 15. Accordingly, the deposits adhered to the bottom peripheralportion and the side edge portion of the wafer W become ashed. However,a considerable time period is required to completely remove the depositsand, in some cases, the deposits are not completely removed.

Meanwhile, if the deposits are adhered to the bottom peripheral portion(and the side edge portion) of the wafer W, they are separated therefromin a post-process to be a cause of particles. Further, in a chemicalpolishing process as the post-process, portions to which the depositsare adhered are stressed, thereby deteriorating polishing accuracy.Accordingly, the wafer W that has gone through the ashing process issubjected to a cleaning process using cleaning fluid in a cleaningvessel. In this case, the deposits detached from the wafer W may beintroduced into the cleaning vessel and transcribed on another wafer, sothat an exchange cycle of the cleaning fluid in the cleaning vesselneeds to be frequently performed. In order to sufficiently remove thedeposits during the ashing process after the etching process, it isconsidered to extend the ashing time to allow the plasma to reach thebottom peripheral portion of the wafer W. In this case, however,depending on types of the insulating film, the film may be changed inquality.

As for an interlayer insulating film, for example, a SiOC film, i.e., acompound of silicon, oxygen and carbon, is widely used due to its lowdielectric constant. However, if the film is exposed to an oxygen plasmafor a long time, a surface thereof becomes oxidized, thereby changingSiOC to SiO₂. The SiO₂ is removed in a post-cleaning process, resultingin a wider line width. Further, the increase in the ashing timedeteriorates a throughput thereof.

A conventional sequence of the plasma processing includes the steps of:stopping a supply of a thermally conductive gas after a specificprocessing is performed by using a plasma; stopping an application of achuck voltage to the electrostatic chuck; and stopping a supply of apower for generating the plasma (see, e.g., Japanese Patent Laid-openPublication Nos. H4-290225 and H8-153713). However, there is notdisclosed nor suggested any process after the processing describedabove.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a plasmaprocessing method and apparatus, wherein when ashing process isperformed by using a plasmarized gas containing O₂ after an etchingprocess has been performed on a substrate by using a plasma, depositsadhered to the substrate during the etching process can be sufficientlyremoved in a short time period.

In accordance with one aspect of the invention, there is provided aplasma processing method for performing a plasma processing on asubstrate mounted on a mounting table installed in an airtightprocessing chamber, the mounting table having a smaller size than thesubstrate, the method including the steps of: mounting the substratehaving a surface, on which a resist mask is formed, on the mountingtable and then electrostatically adsorbing the substrate on the mountingtable by applying a voltage to an electrostatic chuck; etching thesurface of the substrate by using a plasma of an etching gas whilecooling the substrate by way of transferring a heat of the substrate tothe mounting table through a thermally conductive gas supplied between atop surface of the mounting table and a bottom surface of the substrate;stopping the supply of the thermally conductive gas; and ashing theresist mask on the substrate by using a plasma of an ashing gascontaining O₂.

The present invention preferably includes a step of stopping the voltageapplication to the electrostatic chuck after stopping the supply of thethermally conductive gas, wherein the ashing process is performed on thesubstrate under such conditions. This is because if the application ofthe voltage to the electrostatic chuck is stopped in advance, thesubstrate is lifted up by the thermally conductive gas. Even though thesupply of the thermally conductive gas and the voltage application tothe electrostatic chuck are stopped simultaneously, this is alsoconsidered to be included in the descriptions “the voltage applicationto the electrostatic chuck is stopped after the supply of the thermallyconductive gas is stopped” of the present invention if the substrate isnot lifted up. In this case, the etching gas is a compound of carbon andfluorine, for example. Further, a film to be etched is a film containingO₂, e.g., a silicon oxide film, an SiOC film or the like.

In accordance with another aspect of the invention, there is provided aplasma processing apparatus including: a mounting table having a coolingfunction, the mounting table being installed in a processing chamber andhaving a smaller size than a substrate; an electrostatic chuck installedon the mounting table, for electrostatically adsorbing the substrate; apower supply unit for applying a voltage to the electrostatic chuck; athermally conductive gas supply unit for supplying a thermallyconductive gas between a top surface of the mounting table and a bottomsurface of the substrate, wherein after the substrate having thereon aresist mask is mounted on the mounting table and then electrostaticallyadsorbed by the electrostatic chuck, an etching process is performed ona surface of the substrate by using a plasma while the thermallyconductive gas is supplied; and a control unit having a programincluding an instruction for stopping the thermally conductive gassupply of the thermally conductive gas supply unit after the etchingprocess is completed, and an instruction for ashing the resist on thesubstrate by using a plasma of an ashing gas containing O₂.

Preferably, the program further includes an instruction for turning offthe power supply unit to stop the voltage application to theelectrostatic chuck after the supply of the thermally conductive gas isstopped and before the resist mark is ashed.

In accordance with still another aspect of the invention, there isprovided a storage medium for storing therein the program.

In accordance with the present invention, the ashing process after theetching process is performed while stopping the supply of the thermallyconductive gas to the bottom surface of the substrate. The thermallyconductive gas is used for transferring the heat of the substratereceived from the plasma to the mounting table during a plasmaprocessing. Thus, if the supply of the thermally conductive gas isstopped, the heat transferred from the substrate to the mounting tableis reduced. Accordingly, the ashing process is performed under a hightemperature of the substrate, thereby improving the deposit removalefficiency. Moreover, by stopping the supply of the thermally conductivegas, the plasma can easily flow through the gap between the substrateand the focus ring into the bottom side of the substrate. Therefore, thedeposits can be sufficiently removed by the ashing process in a shorttime. As a result, an introduction of particles into a cleaning vesselis suppressed and the ashing time is shortened, thereby enabling toreduce defects on the film of the substrate. Besides, if the voltageapplication to the electrostatic chuck is stopped during the ashingprocess, the gap between the substrate and the mounting table isincreased. Accordingly, the heat transfer efficiency from the substrateto the mounting table deteriorates, so that a temperature of thesubstrate increases. As a result, the deposit removal efficiency isfurther enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following description of preferred embodiments,given in conjunction with the accompanying drawings, in which:

FIG. 1 shows a vertical sectional view of a plasma processing apparatusin accordance with a preferred embodiment of the present invention;

FIG. 2 describes an explanatory diagram of a mounting table of theplasma processing apparatus;

FIG. 3 provides a flow chart illustrating a wafer processing process ofthe plasma processing apparatus;

FIG. 4 represents an explanatory diagram depicting measured portions ofdeposits in experiments conducted to confirm effects of the presentinvention;

FIGS. 5A to 5D offer a characteristic diagrams showing results of theabove experiments;

FIG. 6 presents an explanatory diagram of a conventional plasmaprocessing apparatus; and

FIG. 7 depicts an explanatory diagram describing a status of aperipheral portion of a plasma-processed wafer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of a semiconductor manufacturing apparatus of thepresent invention will be described with reference to FIGS. 1 and 2.Reference numeral 2 indicates an airtight processing chamber made of aconductive material, e.g., aluminum or the like, wherein the processingchamber 2 is grounded. Further, an upper electrode 3 serving as a gasshower head, i.e., a gas supply unit for introducing a specific gas, anda mounting table 4 serving as a lower electrode for mounting thereon asubstrate, e.g., a wafer W, are disposed to face each other in theprocessing chamber 2.

The mounting table 4 is formed to have a smaller size than the wafer Wsuch that a mounting region of the mounting table 4, on which the waferW is mounted, is set to be smaller than a size of the correspondingwafer W. Therefore, a peripheral portion of the wafer W mounted on themounting table 4 is outwardly protruded by, e.g., 1.7 mm to 2.0 mm.Further, a gas exhaust line 21 is connected to a bottom portion of theprocessing chamber 2, and a vacuum exhaust unit, e.g., a vacuum pump 22such as a turbo molecular pump, a dry pump or the like, is connected tothe gas exhaust line 21. Furthermore, an opening 23 a forloading/unloading the wafer W is provided in a sidewall of theprocessing chamber 2, wherein the opening 23 a has an openable/closablegate valve 23.

A plurality of gas diffusion holes 32 communicating with a gas supplyline 31, e.g., a piping, are formed in a bottom surface of the upperelectrode 3, so that an etching gas or an ashing gas as a specificprocessing gas can be sprayed therethrough toward the wafer W mounted onthe mounting table 4. The distal end of the gas supply line 31 isconnected to a gas supply system 33. Specifically, the gas supply system33 includes an etching gas supply system and an ashing gas supplysystem, each having a controller, e.g., a valve, a mass flow controlunit or the like, and a gas supply source (not shown). Further, byswitching flow paths with the help of a flow path switching unit, eitherthe CF-based etching gas or the ashing gas containing O₂ can be suppliedat a specific flow rate via the gas supply line 31.

Connected to the upper electrode 3 is a high frequency power supply unit35 for supplying a high frequency power via a matching unit 34 and a lowpass filter 36. Moreover, an annular shield ring 37 is installed tosurround the upper electrode 3 while being engaged with a peripheralportion of the upper electrode 3.

The mounting table 4 is made of a conductive material, e.g., aluminum orthe like, and has an electrostatic chuck 41 installed on a surfacethereof. A thin electrode 41 a, for example, is provided inside theelectrostatic chuck 41, and a DC power supply 43 is connected to theelectrode 41 a via a switch 42. By applying a DV voltage (chuck voltage)to the electrode 41 a, the wafer W can be electrostatically adsorbed ona surface of the electrostatic chuck 41 by an electrostatic force. Inthis example, the switch 42 and the DC power supply 43 serve as a powersupply unit for applying a voltage to the electrostatic chuck 41.

Further, a focus ring 44 made of, e.g., quartz is installed around theelectrostatic chuck 41 so as to surround a periphery of the wafer Wadsorptively held on the electrostatic chuck 41. Specifically, asdescribed above, the peripheral portion of the wafer W mounted on themounting table 4 is outwardly protruded therefrom, and an innerperipheral surface of the focus ring 44 has a stepped portion whichfaces a bottom surface and a side peripheral surface of such protrudedportion with a slight gap of 1 mm or more formed therebetween.

Provided at a lower portion of the mounting table 4 is a supporting body45 made of, e.g., aluminum or the like. A temperature control fluid path46 of a cooling unit provided in the supporting body 45, and a coolantas a cooling medium flows therethrough. In other words, the top surfaceof the mounting table 4 serves as a cooling plate for cooling the waferW to a predetermined temperature of, e.g., 20° C., by way of taking heatfrom the wafer W whose temperature otherwise increases by a plasmareaction. Reference numerals 47 and 48 indicate a coolant inlet path anda coolant outlet path, respectively. Moreover, although the mountingtable 4 and the supporting body 45 are given different referencenumerals for convenience, the supporting body 45 is a part of themounting table for mounting thereon the wafer W.

Microscopically, the surface of the electrostatic chuck 41 or that ofthe wafer W mounted on the electrostatic chuck 41 has irregularities dueto limitations of a manufacturing precision. Accordingly, even thoughthe wafer is electrostatically adsorbed, a gap is formed between theelectrostatic chuck 41 and the wafer W due to the irregularities and,under a vacuum atmosphere, a heat transfer efficiency through the gapbecomes considerably poor. To that end, a plurality of injectionopenings 5, a part of a thermally conductive gas supply unit is formedin the surface of the electrostatic chuck 41 (see FIG. 2), so that athermally conductive gas, e.g., He gas, for enhancing the heat transferefficiency through the gap formed between the mounting table 4 and thewafer W can be injected through the injection openings 5 toward thebottom surface of the wafer W and diffused from a central portionoutwardly. The injection openings 5 communicate with a thermallyconductive gas supply line 50 penetrating the mounting table 4, thesupporting body 45 and the electrostatic chuck 41. A thermallyconductive gas supply unit 54 is connected to the thermally conductivegas supply line 50 and includes a gas supply source, a valve, a massflow control unit and the like.

Connected to the mounting table 4 are a high frequency power supply 52for applying a bias power via a matching unit 51 and a high pass filter53. Further, installed inside the mounting table 4 and the supportingbody 45 are elevating pins (not shown) capable of transferring the waferW from/to a transfer arm (not shown).

The plasma processing apparatus has a control unit 55 for controlling apressure control unit (not shown) provided at the gas exhaust line 21,the gate valve 23, the high frequency power supply units 35 and 52, theswitch 42, the gas supply system 33, the thermally conductive gas supplyunit 54 and the like. Therefore, while reading a specific processrecipe, the control unit 55 executes a process corresponding to therecipe based on a sequential program 56 stored in a memory as a storagemedium. In such program 56, various instructions are recorded such thatoperations to be described later can be carried out. Further, theprogram in the control unit 55 is installed from the storage medium suchas a compact disk, a flexible disk, a memory stick, a magneto opticaldisk (MO) or the like. Moreover, the storage medium of the presentinvention includes a hard disk, a ROM or the like provided in acomputer, for storing installed programs and developing them in thememory when necessary.

Hereinafter, there will be described of a sequence of a plasmaprocessing on a surface of a substrate, e.g., a wafer W, by using theaforementioned plasma processing apparatus. First of all, the gate valve23 is opened and, then, the wafer W as the substrate is loaded from aload-lock camber (not shown) into the processing chamber 2. Next, thewafer W is mounted on the top surface of the mounting table 4 and, atthe same time, the gate valve 23 is closed. Thereafter, as illustratedin FIG. 3, at a time t1, a CF-based gas, e.g., C₄F₈ gas, as an etchinggas and Ar gas as an inert gas are supplied at respective specific flowrates from the gas shower head as the upper electrode 3 into theprocessing chamber 2. At this time, the etching gas supplied into theprocessing chamber 2 flows along the surface of the wafer Wdiametrically outwardly and is then exhausted through a periphery of themounting table 4.

Next, at a time t2, a power supply unit for the electrostatic chuck 41is turned on, i.e., the switch 42 is closed. Then, by applying a chuckvoltage to the electrostatic chuck 41, the wafer W is electrostaticallyadsorbed. Thereafter, at a time t3, a valve of the thermally conductivegas supply unit 4 is opened, and a thermally conductive gas, e.g., Hegas, is supplied to the bottom surface of the wafer W. Accordingly, thethermally conductive gas flows in and along a slight gap between thebottom surface of the wafer W and the top surface of the mounting table4.

Subsequently, at a time t4, the high frequency power supply units 35 and52 are turned on, so that a high frequency voltage is applied betweenthe upper electrode 3 and the lower electrode 4 as the mounting table,thereby plasmarizing the etching gas. Further, since a bias power isapplied by the high frequency power supply unit 52, active species ofthe plasma impact on the wafer W with high verticality. Accordingly, aSiOC film on the wafer W, for example, is etched by such plasma. At thistime, the plasma flows through the gap between the wafer W and the ringmember 44 toward the bottom side of the wafer W and, thus, a polymerthat is a decomposition product or a reaction product of C₄F₈ gas, isadhered as deposits to the bottom surface and the side edge portion ofthe wafer W.

Although heat is transferred from the plasma to the wafer W, since themounting table 4 is cooled and the thermally conductive gas isinterposed between the wafer W and the mounting table 4, the heattransferred to the wafer W is discharged to the mounting table 4 via thethermally conductive gas. With such heat balance, the temperature of thewafer W can be maintained within a predetermined range from about 10° C.to about 40° C. After the etching process is carried out for a specifictime period, at a time t5, the application of the high frequency poweris stopped by turning off the high frequency power supply units 35 and52 and at the same time the supply of the etching gas is stopped,thereby stopping the etching process. Further, the supply of thethermally conductive gas is stopped slightly later and, at the sametime, an ashing gas containing O₂, e.g., O₂ gas, is supplied from thegas supply system 3 into the processing chamber 2 via the shower head(upper electrode) 3.

Thereafter, at a time t6, the ashing gas is plasmarized by turning onthe high frequency power supply units 35 and 52 and, at the same time, apower supply unit of the electrostatic chuck 41 is turned off (theswitch 42 is turned off). At this time, since the supply of thethermally conductive gas is stopped, the gap between the mounting table4 (the electrostatic chuck 41) and the wafer W is under a high vacuumlevel. Further, since the wafer W is released from the electrostaticallyadsorbed state, the gap is increased. As a result, the thermalconductivity between the wafer W and the mounting table 4 deteriorates,so that the ashing process can be performed while maintaining atemperature of the wafer W within a range of, e.g., 60° C. to 78° C., bythe heat of the plasma.

A resist on the surface of the wafer W is ashed and removed by theactive species of oxygen generated when O₂ gas is plasmarized. However,the deposits adhered to the bottom surface of the wafer W during theetching process are removed by the plasma flowing through the gapbetween the wafer W and the ring member 44 toward the bottom surface ofthe wafer W. At this time, the thermally conductive gas is not sprayedtoward the bottom surface of the wafer W and the gap between the wafer Wand the mounting table 4 increases, so that the plasma is apt to flowthrough the gap toward the bottom surface of the wafer W. Further, dueto a high temperature of the wafer W, the reaction between the depositsand the plasma is accelerated, so that the deposits can be readilyremoved. Moreover, it is preferable to stop the application of the chuckvoltage after the supply of the thermally conductive gas is stopped orat the substantially same time when the supply thereof is stopped.Accordingly, the wafer W released from the electrostatically adsorbedstate can be prevented from being blown away by an injection pressure ofthe thermally conductive gas. Next, at a time t7, the plasma generationis stopped by turning off the high frequency power supply units 35 and52 and, then, an introduction of the ashing gas is stopped slightlylater. Subsequently, the wafer W is unloaded after opening the gatevalve 23. Such series of processes are carried out based on the programstored in the memory in the control unit 55.

In accordance with the aforementioned embodiment, the wafer W is exposedto a plasma of an oxygen-containing etching gas under the condition thatthe supply of the thermally conductive gas to the bottom surface of thewafer W is stopped, thereby removing the deposits adhered to the surfaceof the wafer W during the etching process. Accordingly, as describedabove, the plasma can easily flow into the gap between the wafer W andthe focus ring 44 and the temperature of the wafer W increases due tothe stop of the supply of the thermally conductive gas, so that theremoval of the deposits can be facilitated. Accordingly, the depositscan be sufficiently removed during a short-time ashing process. As aresult, even though the deposits are adhered to the bottom surface ofthe plasma-processed wafer W, the amount of deposits is reduced comparedwith a conventional case, which in turn decreases the amount of foreignmaterials to be introduced into the cleaning vessel in a subsequentcleaning process. Thus, the exchange cycle of the cleaning fluid isextended.

Further, in accordance with the aforementioned embodiment, since theashing process is carried out under the condition that the wafer W isreleased from the electrostatically adsorbed state (i.e., the voltageapplication to the electrostatic chuck 41 is stopped), the wafer W,which was slightly transformed in the electrostatically adsorbed stateto reduce the gap formed between the wafer W and the electrostatic chuck41 due to their surface irregularities, is restored to the originalstate. Accordingly, the gap between the wafer W and the electrostaticchuck 41 is increased. The heat transfer efficiency between the wafer Wand the mounting table 4 deteriorates due to the increased gap, so thatthe temperature of the wafer W increases. Moreover, since the oxygenplasma is apt to flow through the increased gap toward the bottom sideof the wafer W, it is possible to facilitate the removal of the depositsadhered to the bottom surface (and the side edge portion) of the waferW. For the purpose of increasing the temperature of the wafer W in theashing process, it may be considered to provide a heater in the mountingtable 4. In that case, however, a subsequent etching process may beaffected by the temperature variation of the mounting table 4 from apreset temperature. In contrast, the method of this embodiment isadvantageous in that a subsequent etching process is not affected sincethe temperature of the mounting table 4 is maintained.

In the above-described preferred embodiment of the present invention,the supply of the thermally conductive gas and the application of thechuck voltage are both stopped. However, the present invention is notlimited thereto, and only the supply of the thermally conductive gas maybe stopped, which also exhibits the substantially same effects as thosein the aforementioned case. On the other hand, only the application ofthe chuck voltage may be stopped. In this case, in order to prevent thewafer W from blowing away due to an injection pressure of the thermallyconductive gas, it is required to stop the application of the chuckvoltage after reducing a flow rate of the thermally conductive gas. Inthe present invention, since the flow rate reduction of the thermallyconductive gas is substantially same as the stop of the thermallyconductive gas supply and has no particular advantage, it can beconsidered to be included in the conception of the stop of the thermallyconductive gas supply and also in the technical scope of the inventiondefined in the claims to be described later.

In the present invention, an etching gas as a compound of carbon andfluorine may be C₅F₈ or the like. Further, a film containing O₂ as anetching target can be an SiO₂ film or the like.

EXPERIMENTAL EXAMPLES

Hereinafter, there will be described experimental examples conducted toconfirm the effects of the present invention.

Experimental Example 1

This example is an experimental example in which an etching process andan ashing process were performed on the wafer W based on theaforementioned embodiment. While a bias power was applied, an ashing(wafer ashing) time was set to be 15 seconds and 20 seconds. Otherdetailed processing conditions will be described below. It was checkedwhether or not deposits are adhered to the portions illustrated in FIG.4 of the processed wafer and, then, if the deposits were adhered,thickness thereof was measured. Brief descriptions on the measuredportions will be described as follows. An outer edge of a flat surfaceof the wafer W is represented by SECTION A (0.0 mm); a portion located0.5 mm inward from the SECTION A, SECTION B (0.5 mm); a portion located1.0 mm inward from the SECTION A, SECTION C (1.0 mm); a portion locatedon a curved side peripheral surface angularly away by 300 from theSECTION A, SECTION D (30°); and a portion located on the curved sideperipheral surface angularly away by 45° from the SECTION A, SECTION E(45°). The measured results for such portions are shown in FIG. 5A.

-   -   Wafer W: 8 inch (etching target: SiOC film)    -   Etching gas: C₄F₈ gas+Ar gas    -   Etching time: 160˜170 seconds    -   Ashing gas: O₂ gas (1000 sccm)    -   Ashing pressure: 800 mTorr    -   High frequency power in ashing process: 1000 W    -   Bias power in ashing process: 300 W    -   Processing vessel cleaning ashing time (while a bias voltage        apply is stopped): 25 seconds    -   Wafer ashing time (while a bias voltage is applied): 15 seconds,        20 seconds

Experimental Example 2

This example is an experimental example where the processing wasperformed under the same conditions as those in Experimental example 1except that the application of the chuck voltage was not stopped andthat the wafer ashing time was set to be 25 seconds and 35 seconds. Themeasured results of the deposits are illustrated in FIG. 5B.

Comparative Example 1

This example is a comparison example where the processing was performedunder the same conditions as those in Experimental example 1 except thatthe supply of the thermally conductive gas and the application of thechuck voltage were not stopped and that the wafer ashing time was set tobe 25 seconds, 35 seconds, 45 seconds and 60 seconds. The measuredresults of the deposits are depicted in FIG. 5C.

Comparative Example 2

This example is a comparison example where the processing was performedunder the same conditions as those in Experimental example 1 except thatthe wafer ashing was not performed. The measured results of the depositsare shown in FIG. 5D.

(Result and review of Experimental examples 1, 2 and Comparativeexamples 1, 2)

As clearly can be seen from the results of FIGS. 5A to 5D, inComparative example 2 where the wafer ashing process was not performed,the deposits were adhered to SECTIONs A to D. Meanwhile, in Experimentalexamples 1, 2 and Comparative example 1 where the wafer ashing processwas performed, it is noted that deposits were removed by the waferashing process in view of the reduced thickness of the deposits.Specifically, in Experimental example 1 where the supply of thethermally conductive gas and the application of the chuck voltage werestopped, the deposits remained after the ashing process for 15 seconds,but no deposits remained after the ashing process for 20 seconds. InExperimental example 2 where only the supply of the thermally conductivegas was stopped, the deposits remained after the ashing process for 25seconds, but no deposits remained after the ashing process for 35seconds. Meanwhile, in Comparison example 1 where the supply of thethermally conductive gas and the application of the chuck voltage werenot stopped, the deposits were removed only by the ashing process for 60seconds. From the above results, it has been confirmed that a depositremoval efficiency can be improved by stopping the supply of thethermally conductive gas and further enhanced by stopping both of thesupply of the thermally conductive gas and the application of the chuckvoltage. Moreover, the enhanced removal efficiency can result in areduction of the ashing time.

While the invention has been shown and described with respect to thepreferred embodiments, it will be understood by those skilled in the artthat various changes and modification may be made without departing fromthe spirit and scope of the invention as defined in the followingclaims.

1. A plasma processing apparatus comprising: a mounting table having acooling function, the mounting table being installed in a processingchamber and having a smaller size than a substrate; an electrostaticchuck installed on the mounting table, for electrostatically adsorbingthe substrate; a power supply unit for applying a voltage to theelectrostatic chuck; a thermally conductive gas supply unit forsupplying a thermally conductive gas between a top surface of themounting table and a bottom surface of the substrate, wherein after thesubstrate having thereon a resist mask is mounted on the mounting tableand then electrostatically adsorbed by the electrostatic chuck, anetching process is performed on a surface of the substrate by using aplasma while the thermally conductive gas is supplied; and a controlunit having a program including an instruction for stopping thethermally conductive gas supply of the thermally conductive gas supplyunit after the etching process is completed, and an instruction forashing the resist on the substrate by using a plasma of an ashing gascontaining 0₂.
 2. The plasma processing apparatus of claim 1, whereinthe program further includes an instruction for turning off the powersupply unit to stop the voltage application to the electrostatic chuckafter the supply of the thermally conductive gas is stopped and beforethe resist mark is ashed.
 3. A storage medium for storing therein theprogram described in claim 1
 4. A storage medium for storing therein theprogram described in claim 2.